Constrained depth of sculpting
Maybe this can be of help you.

you might use a solidify modifier to a certain seize, on a copy of your object.
Then in blender 2.82 in sculpting there is a remesh option. (top right main drawing window) this does do a voxel based remeshing of your model.
You then have a model that is a certain seize larger, thanks to that remisher it hasnt got wrong inner faces (its only the outside).

Then you can use this object in boolean operations (maybe first substract it from a cube, then use that cube shape to remove outsides from your object (ea double anti modelling).

Be aware though that boolean can have its own complexity errors (make sure to have normals recalculated outside before you start using it on all objects).